新建switch.js,内容如下：
var imgs = [
"https://mlabs.gitee.io/pics/webp/tiankong002-mid.webp",
"https://mlabs.gitee.io/pics/webp/wallhaven-gp1q87.webp",
"https://mlabs.gitee.io/pics/webp/shanshui007small.webp",
"https://mlabs.gitee.io/pics/webp/shenlin001-small.webp",
"https://mlabs.gitee.io/pics/webp/shanshui005-small.webp",
"https://mlabs.gitee.io/pics/webp/shanshui005-mid.webp",
"https://mlabs.gitee.io/pics/webp/shanshui004-small.webp",
"https://mlabs.gitee.io/pics/webp/shanshui003-samll.webp",
"https://mlabs.gitee.io/pics/webp/jianzhou001-small.webp",
"https://mlabs.gitee.io/pics/webp/wallhaven-exvvqk.webp",
"https://mlabs.gitee.io/pics/webp/tianyuan001-small.webp",
"https://mlabs.gitee.io/pics/webp/yuzhou001-small.webp",
];
var index=Math.floor(Math.random()*imgs.length);;
var img = imgs[index];
document.write("<BODY BACKGROUND="+img+" no-repeat>");
新建switch.html,内容如下：
<!DOCTYPE html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1.0,maximum-scale=1.0,minimum-scale=1.0,user-scalable=no">
<title>Switch</title>
<script src="./switch.js"></script>
<style>
body {
background-color: #efefef;
background-repeat: no-repeat;
background-attachment: fixed;
background-position: center 0;
background-size: cover;
}
</style>
</head>
<body>
</body>
</html>